1. Field of the Invention
This invention pertains to air-carbon arc cutting and gouging torches suitable for use in a metal foundry for cleaning riser pads, sprues, fins and other excess or unwanted surface material or defects from large metal castings. An air-carbon arc cutting and gouging torch operates by providing means to position a carbonaceous electrode (e.g. graphite) relative to a workpiece so that an electric arc can be struck and maintained between the electrode and the workpiece. As metal melts under the influence of the arc a stream of high pressure air directed along the electrode forcibly removes the molten metal from the influence of the arc. Thus, in the hands of a skilled operator unwanted metal or nonmetallic substances entrapped in the surface of a casting or metal object can be removed.
2. The Prior Art
The Air-Carbon Arc Cutting and Gouging method was first described in U.S. Pat. No. 2,706,236.
After the basic process was discovered a special torch for use in the foundry was developed and is disclosed in U.S. Pat. No. 2,726,309. The torch disclosed in the '309 patent is of the fixed-head design suitable for positioning large diameter electrodes in relation to a workpiece. Air flow through the torch to ports on either side of the electrode is controlled through a spring loaded valve which is opened by insertion of the electrode. The valve element includes a hemispherical end for contacting the electrode. As is common with all air-carbon arc cutting and gouging torches air and electric current are brought to the torch by means of a coaxial cable, comprising an inner cable carrying electrical energy and an outer insulating coating (e.g. rubber) with a space between the inner cable and outer cable to carry air under pressure. In the torch of the '309 patent current is carried through the valve plunger to the electrode. A torch according to the '309 patent required air having a source pressure of at least 80 psi and preferably 100 psi in order to operate efficiently. In view of the large diameter electrode used for cleaning heavy castings, large current was required to operate the process efficiently. Because of large current densities the torch frequently overheated thus causing operator fatigue and loss of process efficency because of frequent work stopages to allow the torch to cool.